Yes, it is expensive if BMW does it (about $750, but I had to negotiate them down from $1,200). It is complicated because a lot of the rear and the back seats have to be taken out to do it. It takes 3 hours (even after they are "trained" ie. after they have done someone elses.)

I have heard that the electrical portion of your BMW warrenty may not be honored if someone other than a BMW dealer does the work.

All that said, it is a nice looking piece of equipment after installation.